Adding exterior insulation to 100 yr old house – added risk for rot where framing contacts foundation?
Going to add exterior insulation (spray foam likely) over 1 layer of siding. The house has a rubble foundation with no capillary break between the foundation and the framing. The ends of the floor joists are embedded in the foundation.
The house had 2 layers of siding. I’ve removed the outer layer to expose the inner and found the inner siding and sheathing rotted at the bottom of the wall where it covered the band joist and sill. See pictures. Luckily, the joist itself is in good shape.
I’m concerned that the added external insulation will compromise the drying potential of the framing that’s in contact with the foundation. Adding a capillary break is not feasible. Is drying to the interior going to be enough? What if we later insulate the basement; special approach for the area of the floor joists?
Basement is currently uninsulated and moderately heated (forced air furnace in basement has 1 duct for the basement.
We are considering excavating the perimeter of the foundation per Joe Lstiburek’s article:
Seems this is the best defense – keep the basement walls as dry as possible. Any other opportunities/options we should consider?
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